While on the surface, this is a pretty minor deal, there are some interesting subtexts here. First of all, this is a "challenge trade"...the Rangers traded their disappointing outfield prospect for Philly's disappointing outfield prospect. These sorts of deals are fairly rare -- teams generally prefer to stay with the guy they know and have invested in, rather than swap for the same thing from another organization -- but even after getting burned on the John Danks/Brandon McCarthy trade, Daniels pulled the trigger on a similar deal.
Secondly, though, this highlights what has been a Daniels hallmark in terms of building the minor league system...going after the "toolsy" guy. Mayberry was kind of a curious pick when the Rangers took him in 2005 out of Stanford, a guy with big power potential but whose swing was going to have to be rebuilt. Golson was an athlete the Phillies took out of Connally High School in Austin the year before, a guy with tons of tools that had to be turned into skills. Swapping the guy who does little besides hit for the guy with all sorts of attributes, but doesn't hit, was sort of a foreshadowing for what Daniels would be doing the next several years in terms of targeting amateur talent.
In any case, the Rangers ended up trading Golson a year later to the Yankees for Mitch Hilligoss, and he's bounced around in the minors for the last few years, while Mayberry has been a serviceable fourth outfielder for the Phillies. The guy the Rangers viewed as having high bust potential but some possibility of being really good if things clicked ended up busting, and the guy the Rangers viewed as having a low ceiling ended up being a major league bench player.